Electronic Filter Setting Effects on Parameters of Nerve Conduction Studies

Pyun, Sung Bom; Kwon, Hee Kyu; Lee, Hang Jae

Abstract

OBJECTIVE
To investigate the influence of electronic filter setting change on the parameters of motor and sensory nerve conduction studies. METHOD: Median motor and sensory nerve conduction studies were performed in 25 neurologically healthy adult subjects with a mean age of 29 years (range, 20~50). Compound muscle action potentials (CMAPs) and sensory nerve action potentials (SNAPs) were recorded after fixing the low frequency filter cutoff value of 1 Hz, 10 Hz, 100 Hz and 300 Hz and by changing high frequency filter cutoff level from 10 KHz to 0.5 KHz. Onset and peak latency, amplitude of CMAPs and SNAPs were measured and the area of CMAPs were also recorded. Dantec Counterpoint MK2 machine was used. Skin temperature was maintained at 34degrees C or above.
RESULTS
As the high frequency filter was changed from 10 KHz to 0.5 KHz, the mean amplitude of SNAPs and CMAPs decreased by 33.5%, 3.3%, respectively. Onset and peak latency prolonged significantly below the high frequency filter level of 2 KHz (p<0.01). When the low frequency filter was varied form 1 Hz to 300 Hz, large differences were seen in amplitude (69.7%) and area (86.5%) of CMAPs and amplitude of SNAPs (36.6%) (p<0.01), but onset latency was not changed. Peak latency of CMAPs decreased by 20.8%, however, the peak latency of SNAPs reduced slightly (1.4%) (p>0.01).
CONCLUSION
Significant alterations in parameters of CMAPs and SNAPs were produced by modification of filter setting. Optimum filter setting is recommended in nerve conduction study and filter parameters must remain constant when determining normal values and when performing serial studies on patients.